1. Field of the Invention
This invention relates to low-foaming nonionic surfactants and, more particularly, to low-foaming nonionic surfactant compounds which are especially suitable for use in automatic dishwashers and to automatic dishwashing detergent compositions which contain such surfactant compounds.
2. Description of the Prior Art
Detergent compositions containing, in combination, alkaline salts such as sodium silicate and sodium carbonate, an alkaline polyphosphate such as sodium tripolyphosphate, a low-foaming, chlorine-compatible nonionic surfactant, and a chlorine containing compound that provides a hydrochlorite ion in solution are well known and have particular utility in machine dishwashing.
There are many different views on how dishwashing detergents function, but there seems to be general agreement on several points, to wit: (1) the main cleaning is done by the alkaline salts whether by emulsification, saponification, sequestering hard water ions and/or other mechanisms; (2) the active chlorine compound is aimed principally at protein soil but also serves as a destainer and germicide; (3) solubilized protein soil is a main cause of foaming problems; and (4) the surfactant provides optimum cleaning and good spotting and filming results while also providing defoaming power in the presence of foam producing food soil, but the use of auxiliary foam depressants is generally preferred to achieve optimum foam suppressing characteristics. Thus, while dishwasher detergents may clean by a number of processes, the combination of requirements for surfactants that are employed in such detergent compositions are well established. The surfactant must be low foaming and be capable of defoaming food soils; it must have a low cloud point (generally less than about 30.degree. C.) so that it can function as a foam suppressor by separating from solution under hot water temperature (e.g. about 60.degree. C.) but at the same time be sufficiently soluble in the wash liquor to provide wetting; it must be compatible with active chlorine and not markedly decompose those chlorinated compounds used in detergent compositions; and it must have good wetting characteristics to give good spotting and filming results.
Automatic dishwater detergents containing nonionic surfactants of alkoxylated alcohols having block oxypropylene groups and random mixtures of oxyethylene/oxypropylene groups have been disclosed. U.S. Pat. No. 4,272,394 (Kaneko I) and U.S. Pat. No. 4,306,987 (Kaneko II) describe a wide variety of alkoxylated alcohol surfactants including those containing an oxyalkylene block, oxyethylene/oxyalkylene mixture, oxyalkylene block structure. European Patent No. 19, 173 (BASF) discloses a C.sub.9 /C.sub.11 oxyalkylated alcohol having a block oxypropylene, oxyethylene/oxypropylene mixture, having oxyalkylene molar ratios of 2:2 to 3:2 respectively. This latter patent discloses that these structures are derived from West German Printed Publication No. 1, 645,011, which corresponds with U.S. Pat. No. 3,770,701 (Cenker, et al.). None of these patents, however, discloses a nonionic surfactant having the particular structure defined by the claims of the present invention. At their best, the two Kaneko patents describe nonionic surfactants having additional block oxyalkylene groups. The latter two patents describe nonionic surfactant structures having different oxyalkylated alcohols and oxyalkylene ratios from those claimed in the present invention.
Other nonionic surfactants have been used commercially or suggested as meeting these requirements such as, for example, the polyethoxylated octylphenols and polyoxyalkylene glycols disclosed in U.S. Pat. No. 3,936,386 (Corliss et al.); the particular C.sub.17 -C.sub.19 polyethoxylates disclosed in U.S. Pat. No. 4,188,305 (Halas) and U.S. Pat. No. 4,199,468 (Barford et al.); the mixture of an ethylene oxide adduct of nonylphenol or a secondary alcohol and a block oxyethylene/oxypropylene condensate disclosed in U.S. Pat. No. 3,549,539 (Mallows); and the variety of nonionic surfactants disclosed in U.S. Pat. No. 3,314,891 (Schmolka et al.), U.S. Pat. No. 4,136,045 (Gault et al.), and U.S. Pat. No. 4,169,806 (Davis et al.).
While some of these surfactants have received commercial acceptance in various mechanical dishwasher detergent compositions, it would be desirable if a surfactant was developed which exhibited even further improvements in foam suppressing characteristics so as to minimize or eliminate the need for an auxiliary foam suppressing agent, and/or in wetting properties so as to enhance spotting and filming characteristics.